Slides for my screencast of how to make an iPhone application that can parse and present XML data.

1. iOS XML Parser
Evan Johnson - Boniface Designs

2. Objective
Create and iPhone application that downloads
and parses XML data

3. Steps
Create our XML Data
Create a View-based Application

4. XML File
XML: Extensible Markup Language, a metalanguage that
allows users to define their own customized markup
languages.
My XML file will contain the following:
Root Element: <element>
Child Element: <elements>
Attribute: myData

5. XML File
<?xml version=”1.0”?>
<elements>
<element myData=”XML Parsed Successfully” />
</elements>
I am going to save this file as “xmltest.xml” and upload it to my server. If
you want, you can skip creating an XML file and use mine. It is located at:
http://www.bonifacedesigns.com/tuts/xmltest.xml

6. iOS Methods
NSURLConnection
The NSURLConnection will allow us to download the XML file and
communicate with the server.
NSXML Parser
The NSXMLParser methods will help us access the data stored in the
XML file.
Delegate: NSXMLParserDelegate

7. iOS Properties
NSMutableData
We will create an NSMutableData object to store the XML data that we
download
UILabel
I will present the downloaded data in a label on the applications screen
UIButton
A UIButton tap action will start the connection to download the XML
data

8. Steps
Now that we have created our app, we need
to make a connection to load our XML data.
We will do that with the following:
NSURLRequest
I will store the following connection data in a NSURLRequest object:
URL Path to XML file, cache policy, and the timeout interval.
NSURLConnection
After creating the NSURLRequest object, I will initiate my connection

9. Make the request
// Request data from URL
NSURLRequest *theRequest = [NSURLRequest requestWithURL:
[NSURL URLWithString:[NSString stringWithFormat:@"http://
www.bonifacedesigns.com/tuts/xmltest.xml"]]
cachePolicy:NSURLRequestUseProtocolCachePolicy
timeoutInterval:60.0];
Above is the NSURLRequest. Notice that the request utilizes a URL from a
string. The URL is where the XML file I created earlier is hosted. I am using
default settings for the cache policy and time out interval.

10. Start the connection
// Start loading data
NSURLConnection *theConnection = [[NSURLConnection alloc]
initWithRequest:theRequest delegate:self];
if (theConnection) {
// Create the NSMutableData to hold data
receivedData = [[NSMutableData data] retain];
} else {
// Inform the user the connection failed.
}
Now I need to allocate the NSURLConnection and check if it was created. If so,
I will create my NSMutableData object to hold any data that I receive. If not,
you can call upon another method and/or inform the user.
I am going to place this code and the NSURLRequest code in a method that
will be called when my UIButton is tapped.

11. Connection Response
Received
- (void)connection:(NSURLConnection *)connection
didReceiveResponse:(NSURLResponse *)response
This response is usually received before any data has been loaded. I am
going to reset my NSMutableData object encase the server reset in the
middle of of my connection.

12. Connection Received
Data
- (void)connection:(NSURLConnection *)connection
didReceiveData:(NSData *)data
Our XML data might be loaded incrementally. This response is called
whenever data is loaded. I need to append this data to my NSMutableData
object.

13. Connection Failed!
(uh-oh)
- (void)connection:(NSURLConnection *)connection
didFailWithError:(NSError *)error
When a connection fails, this method will be called. We need to release our
connection, release our NSMutableData object, and possibly inform the
user.

14. Connection Finished
- (void)connectionDidFinishLoading:(NSURLConnection
*)connection
If everything works properly and our data is successfully loaded, this
method will be called. We need to initiate our parser (which I will do in a
separate method), and release our connection.

15. Steps
Create our data parser
Parse our data
Handle the data

16. Initiate our parser
NSXMLParser *dataParser = [[NSXMLParser alloc]
initWithData:receivedData];
In a method I will create (called startParsingData:), I will initiate the XML
parser with the method above. I will also assign a delegate to the parser
(self), tell the parser to parse my data, release the parser, and release the
NSMutableData object containing my data.

17. Parse Our Data
- (void)parser:(NSXMLParser *)parser didStartElement:(NSString
*)elementName namespaceURI:(NSString *)namespaceURI
qualifiedName:(NSString *)qName attributes:(NSDictionary
*)attributeDict
The above method will be called once our data is parsed. The method
gives us access to a number of variables, but we are mainly interested in
the elementName and attributeDict. The elementName is where we can
access the XML root and/or child element names. The attributeDict is a
NSDictionary that will store all of the attributes for our elements.

18. Parser Failed
- (void)parser:(NSXMLParser *)parser parseErrorOccurred:
(NSError *)parseError
The above method will be called if the parser has any errors. If the parser
fails, you can then notify the user and/or call upon another method. We
will just be notifying the user with the UILabel we created earlier.

19. Finally, connect
everything up
Open up our xib file and add a UIButton and
UILabel. Connect these objects to their respective
IBOutlets.